1. Technical Field
Example embodiments generally relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing a toner image on a recording medium and an image forming apparatus incorporating the fixing device.
2. Background Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having two or more of copying, printing, scanning, facsimile, plotter, and other functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a development device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the photoconductor onto a recording medium or is indirectly transferred from the photoconductor onto a recording medium via an intermediate transfer belt; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
Such fixing device may include an endless belt having a decreased thermal capacity to shorten a warm-up time taken to warm up the fixing device to a desired fixing temperature and a first print time taken to output the first recording medium bearing the fixed toner image upon receipt of a print job.
For example, the belt is formed into a loop inside which a heater is situated. A pressing roller situated outside the loop formed by the belt is pressed against the belt to form a fixing nip between the pressing roller and the belt. As the belt and the pressing roller rotate and convey the recording medium through the fixing nip, the belt and the pressing roller apply heat and pressure to the recording medium, fixing the toner image on the recording medium.
As the pressing roller rotates, the pressing roller drives and rotates the belt by friction therebetween. Accordingly, as the belt slips on the pressing roller, the belt may apply an unstable brake to the recording medium conveyed through the fixing nip, creasing the recording medium.
To address this circumstance, JP-H09-197864-A discloses the pressing roller having the diameter that increases continuously from a center to each lateral end in an axial direction of the pressing roller, thus increasing the conveyance speed of the recording medium conveyed over each lateral end of the pressing roller relative to the conveyance speed of the recording medium conveyed over the center of the pressing roller. Accordingly, tension exerted on the recording medium is directed from the center to each lateral end of the pressing roller in the axial direction thereof, preventing the recording medium from creasing.
Before the recording medium is conveyed through the fixing nip, tension exerted on the recording medium is directed from the center to each lateral end of the pressing roller in the axial direction thereof. Conversely, however, while the recording medium is conveyed through the fixing nip, tension exerted on the recording medium is directed from each lateral end to the center of the pressing roller in the axial direction thereof.
Accordingly, as tension directed from each lateral end to the center of the pressing roller in the axial direction thereof is exerted on the recording medium, it may crease the recording medium while the recording medium is conveyed through a downstream position in the fixing nip situated downstream from a center of the fixing nip in a recording medium conveyance direction.